1. Field of the Invention
This invention relates to a process of needling a fibrous web from both sides, in which the fibrous web is formed into an endless web and the latter is needled by being pierced in only one direction.
2. Description of the Prior Art
Conventional plants for needling an endless fibrous web from both sides by needling means for piercing the web only in one direction either require two needling units for piercing the web in mutually opposite directions or must perform two consecutive operations in which the web is intially needled from one side and is then inverted and needled from the other side by the same needling means. The web must be removed from the web-guiding means before it can be inverted so that such a needling process in which the web is pierced only in one direction involves a high expenditure of time and work.
It is known from Published German Application No. 2,058,716 that a fibrous web can be needled from both sides by a single needling unit if the web which has traveled through the needling unit is reversed around a reversing roller and is then returned to the needling unit. A perforated plate extends between the two superimposed courses of the web and the needling unit is operated to needle the advancing and returning courses of the web at the same time from mutually opposite sides. The needling results in a decrease of the thickness and an increase of the length of the web so that the two courses must be moved at different velocities as they are needled. For this reason an endless fibrous web cannot be needled on both sides by that known needling process. Besides, it is not possible to establish the same needling conditions on both sides of the web and the needling process can be used only for relatively thin webs because the length of the needles is limited owing to strength considerations.